In recent years, fitness equipment, including weight lifting apparatus using weight stacks and free weights, have become increasingly popular. There are many types of weight lifting apparatus commercially available in which the user performs various exercises to build up muscle tissue. All of these devices exercise muscle tissue by having the user push or pull against a weight on the apparatus which is connected to bars or other hand or foot devices on the apparatus against which the user pushes or pulls. When such devices are used with proper supervision, it is usually recommended for strength training that a spotting partner assist the user by helping the user to continue to lift the weight in the event that "burn-out" occurs. Burn-out occurs when muscle fatigue sets in or when the user has exceeded his physical limitations and cannot proceed through a portion of the lift. Also, with such apparatus, once the weight is lifted, the device is not designed to provide any force in the reverse direction. In other words, once the weight has been raised against the force of gravity, the user with the force of gravity will return the weights to the original position for the next exercise repetition.
It has been discovered that beneficial effects can be achieved by having the user resist movement of the weights back downwardly, after a positive lift. This is commonly termed a "negative rep". With present lifting apparatus this "negative rep" can be accomplished only if the spotter, who is assisting the user, actually forces the weights downward manually.
Even in situation where a spotter or an assistant is available, a spotter must estimate the amount of aid necessary to assist the lifter. Essentially, this estimate may be in error. Also, unless the spotter is well trained, a jerking action throughout the range of motion can occur.
There is therefore a need for a device that can be used in place of the human training assistant or spotter which would shorten lifting schedules and reduce workout time. Moreover, a mechanical assisting device that is properly designed will actually improve the quality and efficiency of the assists and allow the positive and negative spotting to be fully under the control of the user.